One of the challenges in mineral recovery involves the separation (i.e., liberation) of a desired mineral from the ore in which it is contained. Mineral separation has been performed manually (i.e., by hand picking), gravity separation (e.g., jigs and tables), magnetic separation and froth flotation.
Froth flotation is the most common method of liberating the mineral from the other components of the ore. In flotation, the ore is ground to a relatively fine size, placed as a slurry in a froth flotation tank, and contacted with air bubbles. The chemical and physical properties of the desired and/or undesired (i.e., gangue) minerals (i.e., properties generally are the hydrophobicity and/or hydrophilicity of the minerals) are adjusted to cause either the desired or undesired minerals to attach to the air bubbles. The air bubbles carry the attached minerals upwards into a froth at the top of the slurry. The minerals which are not attracted to the air bubbles settle to the bottom of the tank due to gravity. The froth and attached materials are removed from the top of the tank (typically as the concentrate) and the settled materials from the bottom (typically as the tailings).
Flotation suffers from a number of problems. First, flotation can fail to provide the critical upward flow velocity required for the flotation of large particles. Typically, flotation systems rely on the adhesive forces between the bubble and particle to overcome the force of gravity pulling downwards on the particle. The forces of gravity pulling downwards on larger particles can exceed the adhesive force between the particles and the attached bubbles, thereby causing the larger particles to fall to the bottom of the tank. Second, flotation has a limited ability to recover occluded or partially occluded minerals in middlings particles. "Middling" typically are particles which contain minor amounts of a desired mineral attached to undesired minerals. Because the bubbles selectively attach to the mineral, the area for attachment in a middling particle is relatively small and can be easily overcome by gravitational forces. Finally, particles can be knocked loose from attached bubbles in flotation tanks having a high degree of slurry agitation.
Recently, a new concentration flotation technique, known as air lift concentration, has been developed. Air lift concentration is described in U.S. Pat. No. 4,960,509. In air lift concentration, an upward uniform flow of slurry in a flotation zone counteracts the downward flow of gravity on the particles. The greater the velocity of the uniform upward flow, the heavier the particles that can be floated.
There is a need for a concentration process having the ability to inexpensively produce a relatively high recovery of desired minerals from undesirable minerals. Related needs are to provide a concentration process having the ability to liberate undesired minerals from desired minerals and concentrate relatively large and/or heavy particles and middlings particles.